There are more than 300,000 hip and knee replacement surgeries
performed each year in the United States. Sixty-five percent
of hip replacements and seventy-two percent of knee replacements
are received by people over the age of 65. Because the U.S. population
is aging, the number of hip fractures is expected to exceed 500,000
annually by the year 2040. The average hospital stay for a knee
or hip replacement: 5 days followed by four weeks using a walker.

Bob, a retired veterinarian from Golden, Colorado, knows the
statistics because he's one of them. Between 1978 and 1999 Bob
had two hip replacements and five revisions. "I kept three
or four of them as mementos," he laughs. "I've been
thinking of using them as bookends."

Bob's sense of humor is still intact, but the pain is
no laughing matter. "You go until you can't stand it anymore,"
he says, "and then you have surgery again." And again
and again.

"The problem that faces medicine today is that the current
implants last only about ten years," explains Dr. Frank
Schowengerdt, a friend of Bob's and director of the Center
for Commercial Applications of Combustion in Space (CCACS)
at the Colorado School of Mines. (CCACS is a Commercial Space
Center managed by NASA's Space Product Development program.)
"Surgeons cut out the old joint and glue in a new one,"
continues Schowengerdt. "Time along with wear and tear cause
the glue to deteriorate."

Bob recalls his own experiences: "The glue would loosen
and the joint would pinch a nerve. The pain was intense."

Putting
an end to that kind of suffering is what motivates Schowengerdt
and colleague Dr. John Moore. They're working at CCACS
to make better artificial bones from ceramics--implants
so much like the real thing that they could actually meld with
living bone. Such implants wouldn't come loose and need to be
replaced so often.

Left: A normal hip (left) and an artificial hip implant
(right). Learn
more about hip replacement surgery from MEDLINEplus.

Most artificial bones nowadays are made from hydroxyapatite,
which has the same chemical formula as bone itself. Synthetic
hydroxyapatite, however, is neither as porous as real bone nor
as strong.

Pores are important, says Schowengerdt. They are conduits
for blood flow (blood is generated in bone marrow) and they allow
bones to be strong without being too heavy. Pores also provide
a way for living bone to attach itself permanently to an implant.
"If we get good bone growth into the pores of an implant,
then we've won," says Schowengerdt. It won't matter if the
glue comes loose 10 years later.

The solution, according to Schowengerdt,
is ceramics. He and Moore believe it's possible to synthesize
ceramic materials with the right combination of strength and
inter-connected pores to mimic real bone. Indeed they've developed
a process in their Colorado laboratory that looks promising.

"Making ceramic bones isn't like making a ceramic coffee
cup," says Schowengerdt. "The process is completely
different." Ordinary ceramics are made from powders mixed
together with a binding agent. They're baked in an oven (about
1000 C), which evaporates the binder and leaves behind a grainy
matrix stronger than the original powders. The chemical formula
remains unchanged. Unlike coffee-cup makers, however, "we
fire our ceramics at a much higher temperature, so that the powders
react to form new substances."

For example, one of the most promising ceramics starts as
a powdery mixture of calcium and phosphate compounds (CaO and
P2O5). Schowengerdt and Moore ignite the
mixture, which burns at 2600 C. CaO and P2O5
react to produce tricalcium phosphate (Ca3(PO4)2),
a substance remarkably similar (chemically) to real bone. The
reaction also yields heat and gaseous by-products that naturally
form bubbly pores.

It's a good start,
says Schowengerdt, but there's more
to do. For one thing, real bones are porous (weak) on the inside
and solid (strong) on the outside. "What we've made is like
the weak interior of a bone; it doesn't yet have a strong outer
layer. We need to learn to control our process to mimic the stratification
of actual bones."

Their technique, called self-propagating
high-temperature synthesis or "SHS," is indeed hard
to control. "During the firing process, the ceramic is molten.
Gases rise and liquids sink. There's a lot of convective motion
that make the reaction unpredictable," says Schowengerdt. "To understand this process, we really
need to do our experiments in a weightless environment where
gravity-driven convection is minimized."

What
happened? No one is sure because those brief periods of weightlessness
didn't allow enough time for probing and tinkering. That's why
Schowengerdt and Moore are looking forward to March 2003, when
a new materials processing facility named "Space-DRUMSTM"
(a device that holds floating molten ceramics motionless using
sound waves) is slated to be installed on the International Space
Station. By remote control from Earth and with the aid of astronauts,
they'll be able to conduct their tests in low gravity for much
longer times than ever before.

"We don't intend to mass produce ceramic bones on the
ISS," notes Schowengerdt. "That would be way too expensive.
But if we can learn more about the role of gravity in pore formation,
we might be able to duplicate our successes in space here on
Earth."

Millions of people will benefit from fewer surgeries and less
pain if this research produces marketable ceramic bone replacements.
But there could be a problem: what to do with all those obsolete
implants?

Bob Hayes has an answer: "They make great bookends."

Editor's Note: The Center for Commercial Applications
of Combustion in Space is a NASA-sponsored Commercial Space Center
(CSC) at the Colorado School of Mines. NASA's Space Product Development
(SPD) program, located at the Marshall Space Flight Center, encourages
the commercialization of space by industry through 15 such CSCs.
Commercial partners for the research described here include Guigne
International, Ltd., BioServe Space Technologies, Sulzer Orthopedics
Biologics and Hewlett-Packard.

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is to help American businesses explore the potential--and reap
the rewards--of doing business in space. Doing this helps bring
the benefits of space down to Earth where it can, and does, enrich
the everyday lives of the American public. "Industry investment
in space is high," says Mark Nall, manager of NASA's SPD
program at Marshall Space Flight Center. "We assist companies
developing experiments and help them explore how space research
can contribute to the growth of their businesses."